The coronary arteries supply the myocardium, or muscle of the heart with oxygen and nutrients. Over time the coronary arteries can become blocked with cholesterol and other material known as plaque. Coronary artery disease results from this buildup of plaque within the walls of the coronary arteries. Excessive plaque build-up can lead to diminished blood flow through the coronary arteries and blow blood flow to the myocardium leading to chest pain, ischemia, and heart attack. Coronary artery disease can also weaken the heart muscle and contribute to heart failure, a condition where the heart's efficiency as a pump is compromised. This state can lead to electrical disorders of the heart that increase the possibility for sudden cardiac death. Coronary artery is the leading cause of death for both men and women in the United States.
There are several different diagnostics that are currently used to assess coronary artery disease and its severity. Non-invasive tests can include electrocardiograms, biomarker evaluations from blood tests, treadmill tests, echocardiography, single positron emission computed tomography (SPECT), and positron emission tomography (PET). Unfortunately, these non-invasive tests do not provide data related to the size of a coronary lesion or its specific effect on coronary blood flow, lesion pressure gradients and fractional flow reserve.
While CT scans and MRI can be used to visualize the size of the lesion, lesion size does not necessarily correlate to the functional significance of the lesion. Therefore, additional assessments have been developed to determine functional significance of coronary artery lesions. Generally, coronary flow velocity (CFV), pressure gradient (PG), coronary flow reserve (CFR), and fractional flow reserve (FFR) are the gold standard for assessments used to determine the functional significance of coronary artery stenosis. These metrics are currently determined using diagnostic cardiac catheterization, a procedure in which a catheter is inserted into an artery in a patient's leg and threaded through the vasculature to the relevant areas of the coronary arteries. FFR is determined by calculating the ratio of the mean blood pressure downstream from a lesion divided by the mean blood pressure upstream from the same lesion. These pressures are measured by inserting a pressure wire into the patient during the diagnostic cardiac catheterization procedure. While this procedure provides an accurate measure of FFR for determining the functional severity of the coronary stenosis, it is only obtained after the risk and cost of an invasive procedure have already been assumed.
FFR can also be estimated based on a highly complex computational fluid dynamics modeling in CT derived, patient-specific coronary models. This approach requires a high level of sophistication, is computationally expensive, and requires that patient-specific data be transmitted out of the hospital environment to a third party vendor. It is expensive and can take several days to obtain results. Additionally, recent data testing this approach to predict actual FFR in a multicenter trial were very disappointing.
It would therefore be advantageous to provide an alternative non-invasive CT based method for assessing hemodynamic parameters such as determining the CFV, PG, CFR, and/or FFR for a given patient's coronary arteries. Such an approach would fundamentally change the practice of clinical cardiology and allow clinicians to clearly identify specific vessels that are resulting in a reduction in the blood flow to the myocardium.